# CVE-2026-89550

## Summary

- **CVE ID:** CVE-2026-89550
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

SUNRPC: svcauth_gss: enforce krb5 token minimum length

svcauth_gss_unwrap_priv() validates only an upper bound on the
wire-supplied opaque length before handing the buffer to
gss_unwrap():

    if (len > xdr_stream_remaining(xdr))
            goto unwrap_failed;
    offset = xdr_stream_pos(xdr);
    ...
    maj_stat = gss_unwrap(ctx, offset, offset + len, buf);

The wire value `len` flows unchanged as the upper bound into the
krb5 unwrap path, so a len in [0, 16] passes this check and is
handed to gss_unwrap(). For a krb5 v2 context that lands in
gss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token
header fields at ptr+4 and ptr+6 and then calls rotate_left()
before any integrity check. With a sub-header length the header
reads run past the token, and _rotate_left()'s `shift %= buf->len`
path can divide by zero when buf->len has been driven to zero by
the truncated token. A header-only token (len == 16) is equally
invalid: with a non-zero RRC field and the opaque blob ending at
the XDR buffer boundary, rotate_left() builds a zero-length
subbuffer, reaching the same division.

Reject the token at the server entry point before it reaches the
krb5 unwrap core. A valid sealed RFC 4121 token must contain
the 16-byte header plus at least some encrypted payload.

Fix by adding a minimum-length check immediately after the
existing upper-bound check:

    if (len <= GSS_KRB5_TOK_HDR_LEN)
            goto unwrap_failed;

## Affected Products

- Linux — Linux (7c9fdcfb1b64c47ed618c103b617af3f86e1239c)
- Linux — Linux (2.6.18)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651)
- [CNA](https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423)
- [CNA](https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c)
- [CNA](https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489)
- [CNA](https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.46%
- **EPSS Percentile:** 39.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._